Aircraft auxiliary power unit assemblies are typically used during ground operation, and as such may be exposed to contaminants, such as soil particles and sand. Low temperature operation may also expose the auxiliary power unit assembly to icing conditions. Contaminants and ice formation may be detrimental to the operation of the auxiliary power unit assembly, particularly when such assemblies include internal combustion engine(s).
Filters may be provided upstream of the internal combustion engine(s); however, such filters may be susceptible to clogging by ice and/or particles, and/or may be hard to access for replacement or repair.